Interfacial stability and contact damage resistance by incorporating buffer layer in thermal barrier coatings

A buffer layer was introduced between the bond and top coats in air-plasma sprayed (APS) zirconia (ZrO2)-based thermal barrier coating (TBC) system, to improve contact damage and interfacial stability. The microstructure is relatively continuous in the TBC system with the buffer layer, showing a step like distribution of Zr element between the top and bond coats. The TBC system with the buffer layer shows less strain than that without the buffer layer in the higher stress regions above about 1.3 GPa, while both TBC systems become soft by forming the top coat in the lower stress regions compared with the substrate. The TBC system with the buffer layer shows the lower stress–strain curves than that without the buffer layer in the thermal exposure with the relatively short dwell time of 1 h, showing the reverse trend with the relatively long dwell time of 10 h. Subsurface damage in the substrate is reduced at both indentation loads of P = 500 N and P = 2000 N by incorporating the buffer layer, independent of thermal exposure condition. The damage zone formed in the TBC system without the buffer layer increases with increasing exposure time, while the damage does not extend far in the case of the TBC system with the buffer layer. In fracture under contact environments, cracking or delamination is developed between the top coat and the buffer layer in the TBC system with the buffer layer, whereas the fracture is created at the interface of the bond coat and the substrate. The buffer layer is more efficient in protecting the substrate from contact environments and enhances the damage resistance of the TBC system.